WASHINGTON—Senate Democrats lost a key vote Tuesday to expand rights of working women to challenge employers on pay discrimination, but the issue will likely linger until at least the November elections as women’s issues take a prominent role in hotly contested races across the country.

As expected, Senator Scott Brown of Massachusetts voted with the rest of his Republican colleagues in blocking the Paycheck Fairness Act, even as his Democratic opponent, Elizabeth Warren, vowed to use his vote against him in her attempt to foil his reelection bid.

Democrats mustered 52 votes for passage, far short of the 60 needed to block a GOP-led filibuster. All 47 Republicans opposed the bill. Senate Majority Leader Harry Reid voted with Republicans as a procedural tactic to allow him to again bring up the measure.

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“It’s the right cause but the wrong bill,” Brown said after the vote.

Other Republican moderates, including Senators Olympia Snowe and Susan Collins of Maine, who Democrats had hoped would support the bill, agreed with the Bay State Republican, saying that the legislation would impose too much of a burden on employers and spawn frivolous lawsuits.

Supporters of the Paycheck Fairness Act had hoped to build on the Equal Pay Act of 1963, and more recently the Lilly Ledbetter Fair Pay Act of 2009, by requiring employers to provide a reason for pay gaps when asked, and bar companies from retaliating against employees who discuss pay.

The $15 million measure would also fund skills-building programs to train women in negotiating better salaries. In addition, the legislation would have established a salary databank that could help regulators better monitor pay gaps between men and women.

American women make about 77 cents for every dollar earned by men, according to data compiled by the US Census Bureau. In Massachusetts, women fare slightly better, making 81 cents for every dollar earned by men.

“With his vote, Scott Brown is telling the women of Massachusetts he thinks it’s okay that they continue to earn less than men with the same education doing the same work. His vote is costing Massachusetts families hard-earned dollars that they can’t afford to lose in these tough times,” Warren said prior to the vote.

It was no mystery which way Brown would be voting. Two years ago, he voted against an identical bill. Tuesday he cast himself as an advocate of equal pay despite his vote. “As a father and husband of women in the workforce, I believe strongly in fair pay,” he said, “and employers who discriminate against women should be prosecuted aggressively.”

As a sign of the growing sensitivity over the women’s vote, three of Brown’s Republican Senate colleagues – all women from New England – came to his defense.

“Today’s vote in the Senate was regrettably more about politics during an election year than about good policy,” said a statement from Collilns, Snowe, and New Hampshire Senator Kelly Ayotte.

Republicans said the proposal would restrict an employer’s ability to reward employees based on performance, provide bonus pay for hazardous work, or differentiate pay rates based on regional standards. And it would subject employers to unlimited compensatory and punitive damages, even for what they said could be unintentional pay differences.

“We already have existing laws, like the Lilly Ledbetter law, which I supported, to provide ways for workers to fight discrimination,” Collins said.

The Ledbetter law widened the ability of women to sue for alleged pay discrimination.

Democrats invited Ledbetter to speak to reporters just outside the Senate chambers. She called herself the “poster child for unequal pay.” The Alabama woman sued her former employer, Goodyear Tire, after she learned that she was paid less than male former co-workers, but the US Supreme Court ruled against her in 2007 because she had filed her claim after the 180-day statute of limitations. Her namesake law reset the clock for bringing lawsuits.

Advocates of the Paycheck Fairness Act said that wider protections were necessary to give women the ability to determine if employers were paying their male counterparts more—and, if so, why?

Massachusetts Senator John Kerry, a Democrat, joined his party in supporting the legislation.

“This is a bedrock economic issue,” Kerry said. “It’s not only a fairness issue or a question of discrimination. This pay gap haunts women their whole lives and hurts their retirement security and their ability to be providers despite doing the same job as men. It’s just beyond me that we can’t even find the votes to have a debate on this legislation.”

Despite the setback, Democrats have talking points to use in campaigns. President Obama had pushed for passage of the legislation, even if there was little doubt about the vote’s outcome.

“I know we lost the vote today, but we’re not going to give up,” said Senator Barbara Mikulski, the Democrat from Maryland who was the lead sponsor of the law.

The US Chamber of Commerce had urged the Senate to reject the legislation.

“Increasing the opportunity for frivolous litigation will only further serve to undermine our nation’s civil rights laws,” the chamber said in a statement released Monday.

Bobby Caina Calvan can be reached at bobby.calvan@globe.com. Follow him on twitter @GlobeCalvan.